Vanadium tetrachloride

Vanadium tetrachloride
IUPAC name	Vanadium tetrachloride Vanadium(IV) chloride
Identifiers
CAS number	[7632-51-1]
PubChem	24273
RTECS number	YW2625000
Properties
Molecular formula	VCl4
Molar mass	192.75 g/mol
Appearance	bright red liquid, moisture sensitive
Density	1.816 g/cm3, liquid
Melting point	−28 °C
Boiling point	154 °C
Solubility in water	decomposes
Solubility in other solvents	chlorocarbons
Vapor pressure	7.9 Pa
Structure
Coordination geometry	tetrahedral
Dipole moment	0 D
Hazards
EU Index	Not listed
Main hazards	oxidizer; hydrolyzes to release HCl
NFPA 704	0 3 2 W
Related compounds
Other anions	vanadium tetrafluoride, vanadium disulfide, vanadium tetrabromide
Other cations	titanium tetrachloride, chromium tetrachloride, niobium tetrachloride, tantalum tetrachloride
Related compounds	vanadium trichloride
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Vanadium tetrachloride is the chemical compound with the formula VCl₄. This bright red liquid is an important starting reagent in the preparation of vanadium compounds. It forms adducts with many donor ligands, for example, VCl₄(THF)₂. It is also the precursor to vanadocene dichloride.

With one more valence electron than diamagnetic TiCl₄, VCl₄ is a paramagnetic liquid. Few chemical compounds are both liquid (at room temperature) and paramagnetic.

VCl₄ is prepared by chlorination of vanadium metal. Notice that VCl₅ cannot be prepared under normal conditions: Cl₂ lacks the oxidizing power to attack VCl₄. In contrast, the heavier analogues NbCl₅ and TaCl₅ are stable and not particularly oxidizing. Of course, VF₅ does exist, reflecting the increased oxidizing power of F₂ vs Cl₂. Indicative of its oxidizing power, VCl₄ releases Cl₂ at its boiling point (standard pressure) to afford vanadium(III) chloride.

Applications

• In organic synthesis, VCl₄ is used to couple phenols. For example, it converts phenol into 4,4'-biphenol.^[1] It is reduced to VCl₃ in the process.

2 C₆H₅OH + 2 VCl₄ → HOC₆H₄–C₆H₄OH + 2 VCl₃ + 2 HCl

This reaction highlights the oxidizing ability of VCl₄, consistent with it being resistant to further oxidation by Cl₂.

• VCl₄ is a catalyst for the polymerization of alkenes, especially those useful in the rubber industry. The underlying technology is related to Ziegler-Natta catalysis, which involves the intermediacy of vanadium alkyls.

• Further reinforcing its high oxidizing powers, VCl₄ reacts with HBr to produce VBr₃. The reaction proceeds via VBr₄, which releases Br₂ at room temperature.^[2]

2 VCl₄ + 8 HBr → 2 VBr₃ + 8 HCl + Br₂

Safety considerations

VCl₄ is a volatile, aggressive oxidant that readily hydrolyzes to release HCl.

References

1. ^ M. K. O’Brien, B. Vanasse, “Vanadium(IV) Chloride” in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York.
2. ^ Calderazzo, F.; Maichle-Mossmer, C.; Pampaloni, G. and Strähle, J. (1993). "Low-temperature Syntheses of Vanadium(III) and Molybdenum(IV) Bromides by Halide Exchange". Dalton Transactions: 655–8.